There has been an increasing appreciation of the importance of environmental pathways for the human-to-human transmission of respiratory, enteric, and other pathogens. These indirect transmission chains may involve water, food, air, and fomites, all of which provide natural points for intervention. There is a need, therefore, to develop transmission models that explicitly describe pathogen dynamics and the dynamics of human contact with pathogens in these environments. We call these environmental infection transmission system (EITS) models. We propose to develop and examine such models across a range of spatial and temporal scales, as determined by agent survivability in different environments and temporal patterns of excretion and exposure. We focus on enteric pathogens as they: 1) exploit a wide range of environmental scales; 2) there exists extensive human and environmental data; and 3) enteric diseases have major global and domestic public health importance. We propose to build upon our work in the past 10 years applying transmission models to microbial risk assessment that has advanced regulatory policy for the USEPA, and more recently through our work in the Center for Advancing Microbial Risk Assessment (CAMRA). Our analyses have included transmission studies in domestic settings such as Cryptosporidium, MRSA, and norovirus in the United States, as well as international settings such as cholera and diarrheal diseases in Haiti, Thailand, and Ecuador. In our work thus far we have examined distinct types of environmentally mediated transmission on a case-by-case basis. Here we will develop a unified framework integrating environmental transmission across a wide range of temporal and spatial transmission scales. Specifically, we propose the following specific aims: 1) To develop an environmental infection transmission systems (EITS) modeling approach that focuses on long timescales, such as waterborne transmission; 2) To develop an EITS modeling approach that focuses on short timescales, such as fomite transmission; and 3) To develop a framework that integrates these diverse transmission pathways that span across a wide range of spatial and temporal scales. As many interventions are environmentally driven (e.g. surface cleaning, drinking water and wastewater treatment) this framework will provide detailed environmental insight and guidance for policy and interventions.